Loop-circuit supervisory system



Patented Dec. 11, 1945 UNITED STATES PATENT OFFICE LOOPQCIRCUIT VSUPERVISOR!'SYSTEM Y EdwinL. Harder,- Forest'llilll, Pm, assiznor to Westinghouse Electric Corporation, VEast Pittsburglalaga corporation o! Pennsylvania Application October 20, 1943, SerlalvNo.- 506,968

2 Claimsf (Cl. 177-311) i Myv inventionrelates toa supervisorysystem for'k a loop-circuiaparticularly for the supervision of Va series-loop proctive-circuit `through a plurality of linear couplers associatedwith the respective Vterminals of a multi-terminal bus or other alternating-.current Aapparatus to be :pro-

A linear. coupler is ka voltage-producing current-responsive means whichiproducesa relaying voltage-proportionate to the current in the terminal-conductor .with which it .is associated. example of such atlinearvcoupleriswto be founrl941 in my Patent 2,241,127, granted May 6, 1

The importance of vthe supervision of the protective circuits of important lines and .buses is now lso wellrecognized that it is perhaps'unnecessaryto point out this need.' Since the linear coupler system isv primarily adapted for the protection of important' buses, the importance of supervising the series loop-circuit which runs from coupler to coupler will readily. be appreciated. Heretofore, a bridge system of supervision rhas vbeen devised lfor the automatic supervision oi'fsuch circuits, in addition to'a manual supervision-system which required the operation of a push-buttonv by the operator. In many cases, however, it is not feasible to apply Vthe bridge type of supervision, and hence theneed hasb'een` felt for some other type of automatic supervislon'of the loop-circuit `It is an object of myinvention to provide an improved supervised loop-circuit for linear couplers, characterized by having a serially connectedy capacitor inthe loop-circuit, and a directcurrent supervisory source and relay connected in shunt around the capacitor.

A further object of my invention is to provide a novel'- kind of supervisory/means for an alter; nesting-current loop-circuit,l for detecting both groundsand open-circuit in the 'loop=circuit.

With the foregoing and other objects in view, myinventimconsists ofthe apparatus, parts, combinations,l systems and methodshereinafter described and claimed, and illustrated in the accompanying drawing, the single ligure ofvwhich is a' diagrammatic view of circuits and apparatus embodying my invention in an illustrative preferred form of embodiment.

- 1' have illustrated my invention a's being utilized in connection with the protection of'a polyph'ase bus i', the various phase-conductors 'of whichare indicated by .the letters A; B and C. The bus is Villustrated ras Ahaving :four polyphase terminals, connected to as many feeders `or polyphaselines Tn' T2', Tiana-T4, through'circuit which are illustrated as being provided withtrip-coils TC whereby the several breakers may/be opened. Each phase of each ofthe bus-terminals has inductively associated therewith a linear coupler LC, or other voltageproducing current-responsive lmeans for deriving a'voltagewhich is, in each case, a substantially identical predetermined function of a terminalcurrent of the apparatus, times an impedance which is substantially constant for all obtainable current-values and which is substantially the same for all terminals. Inactual practice, the linear couplers LC may conveniently be associated with the terminal-bushings (not shown) of 4the respective'circuit-breakers CB. The variouscouplersare distinguished by suilixed numerals-and letters indicative kof the particular terminal and phase with which the coupler is associated.-

I'have illustrated my invention in connection with a three-phase bus, in which it is desirable to have separate summation-means for each of the phases of thebus, for securing an indication oi the vectorial sum of all of the currents enter ing that phase ofthe bus, in al1 of the terminals thereof, so asto obtain an indication of an internal fault on the bus in case the vectorial sum of these terminal currents,l of that phase, should become other than zero. Since the linear coupler is a voltage-producing device, rather than a current-producing device, as is the case with ordinary current-transformers, the summatingmeanstakes the 4form of a series loop, 2, for each phase.

Since the protective devices for the different phases are all alike, my description will be more specifically directed to the phase-A loop-circuit 2, which includes the four phase-A linear couplers LCe-iAtoLCi-IA. The loop-circuit 2 includes analternatingcurrent energy-translating means, in the form of the operating coil of a faultdetectiverelay 3. In accordance with my invention," the loop-'circuit 2 alsoV serially includes a capacitor I, which'is useful, not only as a means for applying my supervisory means, which will be subsequently described, but also as a means which may be utilized to approximately tune the loop 2, or to more or less perfectly neutralize, or compensate for, or even to overcompensate for,v the reactance 'of the Ventire loop-circuit, thus reducing the volt-ampere burden on the respective linear couplers.

The 'fault-'detective 'relay 3 is provided with a makecontact 5which is utilized to energize a tripping "relay B having contacts 1 which energize the respective trip-coils TC of all of the circuit breakers CB, so as to open all of the terminals of the bus I, in the event of a fault on any phase of the bus.

In accordance with my invention, thejseries capacitor 4 of the loop-circuit 2 is shunted by means of a supervisory circuit vwhich includes the operating coil I of Ya polarized supervisory relay II, or other sensitive direct-current relay, having a drop-out contact-member I2 which is utilized to energize an alarm-circuit I3 when the supervisory relay II being shown in itsenergized y position.

The supervisory circuit which ,shunts theseries capacitor 4 includes, in addition tothelop'erating coil I Il of the supervisory relayI I,"adirect current source which is indlcate'dzby itstermi-V j f which is So high that the supervisory current,

which is superimposed upon the loop-circuit 2, is far below the level of sensitivity of thev faultdetective relay 3, so that theaction of the faultdetective relay 3 will not be at all affected Vby the tiny circulating'direct current. -The supervisory circuit is preferably grounded between the resistance I4 and the adjacent battery-terminal (-),asindicatedatl5,. A

Thus, the ventire supervisory circuit may be regarded as including, ilrst, a circuit means for connecting vone terminal ofthe high-resistance portion I Il-I4 of the supervisoryvcircuit to the loop-circuit 2, on one side of the capacitor 4, as indicated at I6: also another circuit-meansin cludng a resistor I'I, for connecting one battery-terminal (-I-) to the loop-circuit on the other side of the capacitor 4, at a point indicated at I 8; and also circuit-means for connecting together, and grounding, the other terminal ofthe high-resistance portion I0-I4 and the other battery-terminal as indicated at I5. vIn this manner, the loop-circuit 2` operates at adirectcurrent supervision-voltage above ground; said voltage being the voltage of the supervisory battery or other direct-current source indicated by the terminals and minus the voltagedrop in the resistor I'I. 5

In operation,v the capacitor 4 is introduced in order to completethe alternating-current loopcircuit, and still open the loop so that av small direct-current can be introduced in the looplfor supervising purposes. In the previously known bridge-type Vsystem of automatic supervision, it was not possible to utilize a series capacitor, because it was necessary for the supervised directcurrent to be able to ow throughout all portions of the supervised circuitfand hence it was not possible to obtain the additionaladvantage of. the cancellation of inductive reactance, which is made possible by the introduction ofthe series capacitor. v

In normal operation,r the battery, indicated by the terminals (-I) and circulates a tiny supervisory direct-current through the high resistance I4, the supervisory-relay coil I0; and the entire loop-circuit 2 other than the capacitor 4, that is, through each of the fourr linear couplers LC--IA to LC4A, and through the operating coil of the alternating-current protectiverelay 3. In case this loop-circuit shouldbecome 4broken. or open-circuited at any.v point, this flow of the tiny supervisory direct current will be interrupted, the supervisory relay II will be deenergized,

and its contact-member I2 will close, to energize the alarm-circuit I3.

My provision of the high resistance I4 and the ground-connection I5, in the supervisory circuit, also makes it possible to utilize the same supervisory relay II to respond to a grounded condition of any portion of the supervised loop-circuit`2. 'This istrue, because the Aimpedance of the portion III- I4 of the supervisory circuit Operating con lo is insufficiently energized, the p 1 which includes the supervisory-relay I0 hasavery considerably higher resistance than the portion II- of the supervisory circuit including the drect-current sourcewhich is represented by the battery terminals I+) and and because the @battery-portion' of this circuit is directly connected, through` a relatively small resistance I'I, between the vloop-connection at I8 and the ground-connection at I5.

Consequently, if any portion ofthe loop-circuit 2v should become grounded, the battery-'conf taining portion I1 of the supervisory circuit would become short circuited, or its 'circuit would become completed through a resistance I1 which is very low as compared tothe resistance I4, assuming that the resistance I 4 is much higher than the resistance of any grounding circuit in the event of a ground on the loop-circuit 2. Thefeffectof e this short-circuiting of the supervisory batterysource, as a result of a ground on the.v protected loop-circuit 2, will thus be to substantiallyv conipletely deenergize the supervisory relay 'I I. thus causing its drop-out contacts I 2 to close, the -same as would be the casein the event oi' an` opencircuit within the protected-loop-circuit 2. I sistance `I'I is ofv such value that a `ground-mult on the loop 2 cannot draw vsuiiicientdirect currentv to trip the protective relay 3. i

While I have indicated but a single illustrative form of embodiment of my invention, I` wish it ,to

be understood that' my invention is susceptible of various alterations, byv way of modications., additions and omissions, Within-the skill of theY said supervisorylcircuit which includes said supervisory relay-means having a high resistance, so high that the supervisory current is far below the level of sensitivity of the alternating-'current energy-translating means Oi' the loop-circuit,- means for connecting one terminal of said highresistance portion of the supervisory circuit to the .loop-circuit on one side of the capacitor, meansfor connecting one terminalof said directcurrent source to the loop-circuit on the other side ofthe capacitor, and means for connecting together, andgrounding, theother terminals vof said high-resistance portion and said source.

2. Supervisory means for ani alternating-'current loop-circuit including alternating-current energy-translating means and a capacitor serially included in .said loop-circuit,- said supervisory The' recurrent, connected between the second terminal of the capacitor and ground, said lower resistance 1 being of such value that a ground-fault on the loop-circuit cannot draw sufiicient supervisory current to actuate the alternating-current energy-translating means of the loop-circuit, and the resistance of the high-resistance circuit-portion being so great that a ground-fault on the loop-circuit causes the supervisory relay-means to drop out.

EDWIN L. HARDER. 

